I am currently running Ubuntu 20.04.1 on an Asus laptop. After I upgraded from 18.04, I installed the correct printer and scanner drivers for my Brother MFC-J805DW. I have no issues with printing. (Everything is on a wireless WAN, and I have no problems with any other devices on the network.)
However, I continue to have communication issues with scanning.
For example, yesterday, I completely uninstalled all Brother drivers, disabled Ubuntu autofinding printers, installed scanner and printer drivers I downloaded from the Brother website. I was able to successfully scan yesterday. (I use gscan2pdf.)
However, today when I tried to scan, I was unable to set the document size in gscan2pdf—nothing appears in the Geometry tab in gscan2pdf. (This has happened before.) So I scanned my document in the default size, which appears to be legal size.
Without closing gscan2pdf I tried to scan a second document. Suddenly, I got a "scanimage: open of device brother4:net1;dev0 failed: Invalid argument" error message. (This has also happened before. I change nothing, and suddenly my computer can't communicate with my scanner.)
What has worked in the past is to reinstall the scanner driver. I then run brsaneconfig4 -a name=Pete model=MFC-J805DW ip=13.13.1.21 to add a network entry. (Yes, my scanner is named Pete. I got tired of just calling it "Scanner".)
When I run scanimage -L I get the following output:
device `brother4:net1;dev0' is a Brother Pete MFC-J805DW
device `escl:http://13.13.1.21:80' is a ESCL MFC-J805DW flatbed scanner
device `net:localhost:brother4:net1;dev0' is a Brother Pete MFC-J805DW
Running dpkg -l | grep Brother shows that the driver is installed:
ii brscan4 0.4.9-1 amd64 Brother Scanner Driver
ii hll2370dwpdrv:i386 4.0.0-1 i386 Brother HL-L2370DW printer driver (lpd/cups)
ii mfcj805dwpdrv:i386 1.0.5-0 i386 Brother Inkjet Printer Driver
Now when I open gscan2pdf, I get three different scanners showing up. However, the Geometry tab is completely blank no matter which scanner I select.
I was able to scan using the first scanner listed in the above list, but again, it automatically defaulted to legal size, and I cannot set a different size.
My main question is, does anybody know what is happening here? Why does my computer lose connection with my scanner? How can I set this up so that I can communicate with it enough to tell it what size my paper is?
(On a side note, if somebody could tell me what an ESCL scanner is, I would pay good money to see that post. U of Google has remarkably little to say about it. And if I could add that as a tag here I would, but I don't have the required reputation, alas.)
